1. Field of the Invention
This invention relates to wireless local network (WLANs) and more specifically to weighted Point Coordination Function (PCF) polling lists for WLAN Quality of Service (QoS) support.
2. Background and Material Information
The Institute for Electrical and Electronic Engineers (IEEE) has developed a standard that defines a protocol for transferring data frames between wireless local area network stations and terminals. This is the IEEE Std. 802.11, IEEE standard for Wireless LAN Medium Access (MAC) and Physical Layer (PHY), 1997, which is herein incorporated by reference in its entirety. The standard defines a MAC layer with two different methods for accessing the wireless interface, the Distributed Coordination Function (DCF) and the Point Coordination Function (PCF). DCF is generally meant for Best Effort traffic delivery, and PCF is generally meant for Real Time traffic delivery. Best Effort traffic is a QoS class of traffic with no specific parameters and with no assurances that the traffic will be delivered across the network to the target device. Real Time traffic refers to traffic conducted in real time, i.e., there is no perceived delay in the transmission of the information or the response to it (e.g., interactive video). The DCF and the PCF are coexisting and the PCF requires that the DCF is implemented. The 802.11 MAC architecture provides the PCF through the services of the DCF.
In DCF, all terminals contend for who may send transmissions next. The fundamental access method of the 802.11 MAC is a DCF known as carrier sense multiple access with collision avoidance (CSMA/CA), which is an adaptation of carrier sense multiple access with collision detection (CSMA/CD) used by Ethernet networks. In a CSMA protocol, a station or terminal that wants to transmit on the wireless local area network WLAN medium, senses the medium to determine if the another station is transmitting (i.e., medium is busy). If not, the transmission may proceed. If the medium is busy, the station defers its transmission till the end of the current transmission and an idle period of time thereafter. The transmitting station may then exchange short control frames (request to send (RTS) and clear to send (CTS) frames) with a receiving station after determining that the medium is idle and prior to data transmission. The control frames message duration is known as the network allocation vector (NAV) and effectively alerts all other stations in the medium to back off for the duration of the data transmission.
In PCF, a point coordinator (PC) is used to coordinate transmissions of the terminals. The point coordinator acts as a polling master and polls all the PCF pollable terminals to determine which terminals may transmit. The PC may be located in an Access Point (AP) that provides wireless mobile terminals (MTs) access to the WLAN. In PCF, a terminal may be a pollable terminal (terminal desiring to be polled) or a non-pollable terminal (terminal not polled by the PC). A terminal that is polled may then transmit only one MAC Protocol Data Unit (MSDU). The terminal must be polled again to transmit for another time. If a particular transmission ends unsuccessfully, the terminal may not retransmit the data until polled again by the PC. Therefore, PCF provides a contention free mechanism for determining which terminal has the right to transmit.
At 802.11 WLAN is based on a cellular architecture where the system is subdivided into cells. Each cell is called a Basic Service Set (BSS), and is controlled by a base station called an Access Point (AP). The DCF and the PCF coexist and operate concurrently within a BSS. DCF may be used for Best Effort traffic delivery and PCF may be used for Real Time traffic delivery.
FIG. 1 shows a timing diagram of the PCF/DCF periods. When a PC is operating in a BSS, the two access methods (DCF and PCF) alternate, with a contention-free period (CFP) 2 followed by a contention period (CP) 4. CFPs and CPs alternate. These periods may be dynamically adjusted on the basis of the amount of polled terminals. Each terminal that has indicated the willingness to be polled, is polled once per CFP. A network allocation vector (NAV) 8 extends the message duration and alerts others in the medium to back off on attempting to gain access to the medium for the duration of the transmission.
Therefore, the IEEE Std. 802.11 defines a PCF basic operation capable of promising non-contested access to the air interface, thus ensuring that long contention times are not possible. However, the standard does not offer any mechanisms for promising more air interface than once per polling period for a particular terminal. Further, current methods do not provide a mechanism for preserving network level Quality Of Service (QoS) in the air interface based on upper layer QoS information.
Accordingly, the present invention is directed to methods and apparatus for weighted Point Coordination Function (PCF) polling lists for WLAN Quality of Service (QoS) support that substantially obviates one or more of the problems arising from the limitations and disadvantages of the related art.
In one aspect, the present invention is directed to a method for weighted polling of terminals in a Wireless Local Area Network (WLAN) that may include: obtaining information related to WLAN terminals; assigning a weighted polling factor to each WLAN terminal based on the information; and polling each WLAN terminal during a transmission period based on the weighted polling factor assigned to each WLAN terminal.
The information may be Quality of Service (QoS) related information. The QoS related information may include billing information, an amount of real time traffic destined from or to at least one WLAN terminal, a user profile of at least one WLAN terminal, and/or an amount of bandwidth consumed by at least one WLAN terminal. Each weighted polling factor may denote a number of times each WLAN terminal is to be polled. Each WLAN terminal may be polled by a Point Coordinator. The Point Coordinator may reside in an Access Point that may provide wireless WLAN terminals access to the WLAN.
The WLAN terminal may be pollable. The transmission period may be an IEEE 802.11 Contention Free Period (CFP). The WLAN terminal may be a mobile terminal. At least one WLAN terminal may be polled at least once during the transmission period. At least one WLAN terminal may be polled at least once during every other transmission period.
In another aspect, the present invention may be directed to a method for transferring data based on weighted polling of terminals in a Wireless Local Area Network (WLAN) that may include: dividing data to be transferred into best effort data and real time data; storing the best effort data in a best effort queue; storing the real time data in a real time queue; obtaining information related to at least one WLAN terminal associated with some real time data; assigning a weighted polling factor to each at least one WLAN terminal based on the information; placing a terminal identification of each at least one WLAN terminal in a polling list at least once based on the weighted polling factor of each at least one WLAN terminal; and polling WLAN terminals whose terminal identification is in the polling list based on a number of times each WLAN terminal identification is listed in the polling list. Each polled WLAN terminal may transfer the associated real time data during a transmission period.
The information may be Quality of Service (QoS) related information. The QoS related information may include billing information, an amount of real time traffic destined from or to at least one WLAN terminal, a user profile of at least one WLAN terminal, and an amount of bandwidth consumed by at least one WLAN terminal. Each weighted polling factor may denote a number of times each WLAN terminal is to be polled. The transmission period may be an IEEE 802.11 Contention Free Period (CFP). The WLAN terminal may be a mobile terminal.
In a further aspect, the present invention may be directed to a Wireless Local Area Network (WLAN) Quality of Service (QoS) system that provides weighted polling of WLAN terminals that includes: a WLAN; at least one access point operatively connected to the WLAN, and at least one WLAN terminal. The access point may include: a real time data queue; a best effort data queue; a data packet classifier where the data packet classifier separates data into real time data and best effort data; a data transfer manager where the data transfer manager stores the real time data in the real time data queue and the best effort data in the best effort data queue; and a polling list. The at least one WLAN terminal may be operatively connected to the at least one access point. The data transfer manager may obtain QoS related information related to the at least one WLAN terminal and assign a weighted polling factor to each at least one WLAN terminal based on the QoS related information. The data transfer manager may place a terminal identification of each at least one WLAN terminal related to some real data in the polling list queue at least once based on the weighted polling factor of each at least one WLAN terminal. The data transfer manager may poll WLAN terminals whose terminal identification is in the polling list queue based on a number of times each WLAN terminal identification is listed in the polling list. Each polled WLAN terminal may transfer the associated real time data during a transmission period.
The transmission period may be an IEEE 802.11 Contention Free Period (CFP). The WLAN terminal may be a mobile terminal. The QoS related information may include billing information, an amount of real time traffic destined from or to at least one WLAN terminal, a user profile of at least one WLAN terminal, and/or an amount of bandwidth consumed by at least one WLAN terminal.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawings.